Abstract
Simple SummaryIt is difficult for Alfalfa alone to obtain a competitive fermentation quality due to its low content of fermentable carbohydrate and great buffering capacity. Sugar cane molasses additives provide a substrate for the rapid accumulation of lactic acid (LA) and pH reduction while increasing the nutritional quality of silage. The present work aims to study the effects of molasses additives on the fermentation quality and taste evaluation of the alfalfa silage. The microbial communities of the alfalfa silage were also described as the explanation for the changes in silages. The study could give directions on improving the fermentation quality of alfalfa silage and achieve long-term preservation.The objective was to study the effects of sugar cane molasses addition on the fermentation quality and tastes of alfalfa silage. Fresh alfalfa was ensiled with no additive (Control), 1% molasses (M1), 2% molasses (M2), and 3% molasses (M3) for 206 days. The chemical composition and fermentation characteristics of the alfalfa silages were determined, the microbial communities were described by 16S rRNA sequencing, and the tastes were evaluated using an electronic tongue sensing system. With the amount of added molasses (M), most nutrition (dry matter and crude protein) was preserved and water-soluble carbohydrates (WSC) were sufficiently used to promote the fermentation, resulting in a pH reduction from 5.16 to 4.48. The lactic acid (LA) content and LA/acetic acid (AA) significantly increased, indicating that the fermentation had turned to homofermentation. After ensiling, Enterococcus and Lactobacillus were the dominant genus in all treatments and the undesirable microbes were inhibited, resulting in lower propionic acid (PA), butyric acid (BA), and NH3-N production. In addition, bitterness, astringency, and sourness reflected tastes of alfalfa silage, while umami and sourness changed with the amount of added molasses. Therefore, molasses additive had improved the fermentation quality and tastes of alfalfa silage, and the M3 group obtained the ideal pH value (below 4.5) and the best condition for long-term preservation.
Highlights
Alfalfa is considered a promising high-quality feed for ruminants due to its good palatability and high protein content [1,2], but suffers a loss of nutrition caused by aerobic deterioration, especially in humid conditions and rainy climates, and needs an efficient way of preservation
lactic acid (LA)/acetic acid (AA) was significantly increased with the amount of added M, indicating that the fermentation of alfalfa silage had turned to homofermentation, which was consistent with previous studies [12]
water-soluble carbohydrates (WSC), as the fermentation substrate, was reduced to around 30 g/kg DM, the value of which was considered the threshold for continuing fermentation, and the pH value was reduced to 5.16
Summary
Alfalfa is considered a promising high-quality feed for ruminants due to its good palatability and high protein content [1,2], but suffers a loss of nutrition caused by aerobic deterioration, especially in humid conditions and rainy climates, and needs an efficient way of preservation. Sufficient fermentable carbohydrates, as the fermentable substrate in the early stage, are crucial for LA production, which reduces the pH value and improves the silage quality [6]. Previous studies have suggested that ensiling alfalfa with high-sugar-content forage crops, such as corn [8] and sweet sorghum [9], could significantly improve the fermentation quality of alfalfa silage. Another strategy is to add cheap sources of exogenous sugar additive, such as molasses (M), which has been widely used to accelerate fermentation and improve the quality of alfalfa silage [10]. The fermentation quality of alfalfa silage prepared with M additive has not sufficiently been studied yet and remains controversial
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